How to build a Shader for Anodized Aluminium
Here's what I have come up with.



The shader consists of a little bit of diffuse mixed into some fairly rough gloss, with a smoother Fresnel gloss mixed in at the end.  I also noticed that the gloss on you reference image has a very slight, yet distinct, variation in reflectance across the phone.  To simulate this I added a noise texture controlling the roughness of the two glossy shaders.

Here is my node layout:


Click to enlarge.

A few notes:


I am using Geometry > Position as mapping coordinates for the noise texture to get even scaling.  Using generated coordinates on an object with a non-cuboidal bounding box results in stretching.
I use an RGB Curves node to bump up the contrast.
All the math nodes just remap the [0,1] range of the texture to the desired ranges for the glossy roughnesses.
The colors in the above node layout are for the gold shader on the right of the render.  The silver one just uses grey in all 3 shaders (light grey for the glosses and slightly darker for the diffuse).